The present invention generally relates to a brake booster. More particularly, the present invention pertains to a vacuum type servo system to be applied to an automobile.
U.S. Pat. No. 5,483,866 discloses a vacuum type servo system that includes a housing in which is formed at least one pressure chamber, a movable wall disposed in the housing to move forward and backward with respect to the housing for partitioning the pressure chamber into a front chamber communicating with a vacuum source and a rear chamber for selectively communicating with the front chamber and the atmosphere, a power piston jointed to the movable wall, an input member arranged in the power piston to move forward and backward with respect to the power piston, and a valve plunger member arranged in the power piston for moving forward and backward integrally with the input member. An atmospheric valve seat is arranged in the valve plunger member and a vacuum valve seat is arranged in the power piston. A control valve is defined by an atmospheric seal portion capable of moving into and out of engagement with the atmospheric valve seat to cut off communication with the rear chamber and the atmosphere upon engaging the atmospheric valve seat and to establish communication of the rear chamber with the atmosphere upon being out of engagement with the atmospheric valve seat, and a vacuum seal portion capable of moving into and out of engagement with the vacuum valve seat to cut off communication between the front chamber and the rear chamber upon engagement with the vacuum valve seat and to establish communication of the rear chamber with the front chamber upon being out of engagement with the vacuum valve seat. An output member outputs to the outside the forward force of the power piston in accordance with the movement of the movable wall. A reaction member transmits member to the output member the forward force of the power piston and an input applied to the input, and applies a reaction of a magnitude corresponding to the output of the output member to move the input member backward. An actuator brings the valve plunger member forward to move the atmospheric valve seat away from the atmospheric seal portion to thereby establish communication between the rear chamber and the atmosphere.
In this known vacuum type servo system, the valve plunger member is moved by activating the actuator separately of the operation of the input member so that the atmospheric valve seat is moved away from the atmospheric seal portion to establish communication between the rear chamber and the atmosphere and accordingly a pressure difference between the front chamber and the rear chamber. When this pressure difference is established between the front chamber and the rear chamber by the activation of the actuator, forward forces are generated at the movable wall and the power piston, and the output member outputs the forward force of the power piston to the outside.
In this vacuum type servo system, however, the flow of atmospheric air into the rear chamber by the activation of the actuator continues until the rear chamber receives the atmospheric pressure so that the output of the vacuum type servo system to be outputted from the output member in accordance with the activation of the actuator reaches a maximum.
It is conceivable that this vacuum type servo system for generating an output by activation of the actuator independently of the operation of the input member can be applied to an automatic braking system that is designed to maintain the vehicle distance, for example, at a predetermined value.
This automatic braking system is typically designed so that when the distance between a running vehicle and a proceeding vehicle becomes shorter than a predetermined distance, for example, braking action in the vehicle is achieved by activating the system without any braking operation of the driver so that the vehicle distance may be kept at a predetermined value. The automatic braking action of this automatic braking system has a tendency not to require a high braking force.
When the aforementioned vacuum type servo system is applied to an automatic braking system such as described above, the actuator is activated when the vehicle distance becomes shorter than the predetermined value. The output is thus generated in the vacuum type servo system to effect the automatic braking operation without any braking operation of the driver, i.e., without any operation of the input member.
However, the braking force to be generated at this time is based on the maximum output that is established in the vacuum type servo system and this rather strong braking force may not be well suited for the automatic braking operation in the automatic braking system. In other words, the known vacuum type servo system described above is not well suited for braking systems which do not require the generation of the maximum output of the vacuum type servo system.
In light of the foregoing, a need exists for a vacuum type servo system that is capable of regulating the output accompanying the activation of an actuator to the maximum output or less than the maximum output.
A need also exists for a vacuum type servo system which is able to control the output accompanying the activation of the actuator within a range lower than the jumping output of the performance of an ordinary brake.
A vacuum type servo system according to one aspect of the invention includes: a housing having at least one pressure chamber formed therein; a movable wall so disposed in the housing as to move forward and backward with respect to the housing for partitioning the pressure chamber into a front chamber communicating with a vacuum source and a rear chamber selected to communicate with the front chamber and the atmosphere; a power piston jointed to the movable wall; an input member so arranged in the power piston as to move forward and backward with respect to the power piston; an atmospheric valve seat arranged in the power piston for moving forward and backward integrally with the input member; a vacuum valve seat arranged in the power piston; a control valve including an atmospheric seal portion capable of coming into and going out of abutment against the atmospheric valve seat for cutting off the communication with the rear chamber and the atmosphere when it comes into abutment against the atmospheric valve seat and for establishing the communication of the rear chamber with the atmosphere when it goes out of abutment against the atmospheric valve seat, and a vacuum seal portion capable of coming into and going out of abutment against the vacuum valve seat for cutting off t-e communication between the front chamber and the rear chamber when it comes into abutment against the vacuum valve seat and for establishing the communication of the rear chamber with the front chamber when it goes out of abutment against the vacuum valve seat; an output member for outputting the forward force of the power piston in accordance with the movement of the movable wall to the outside of the system; a reaction member for transmitting the forward force of the power piston and an input fed to the input member, to the output member and for applying a reaction of a magnitude corresponding to an output of the output member, to move the input member backward; and an actuator for bringing the atmospheric valve seat and the atmospheric seal portion away from each other to establish the communication between the rear chamber and the atmosphere, wherein the input member includes: a front member for coming into abutment against the reaction member; and a rear member capable of moving integrally with the atmospheric valve seat, so that when a predetermined input is fed to the input member, the rear member moves forward by a predetermined stroke with respect to the front member, and so that when the input member is moved backward by a reaction of the reaction member in accordance with the activation of the actuator, the atmospheric valve seat and the atmospheric seal portion can come into abutment against each other to cut off communication between the rear chamber and the atmosphere.
Preferably, the input member and the reaction member are in abutment against each other in an initial state where no input is applied to the input member. The input member preferably includes: a first joint mechanism for joining the front member and the rear member when the rear member moves forward by a predetermined stroke with respect to the front member, so that the front member and the rear member may integrally move forward; and a second joint mechanism for regulating the rearmost position of the rear member with respect to the front member and for jointing the front member and the rear member, when the rear member is at the rearmost position, so that the front member and the rear member may integrally move backward.
The second joint mechanism can be arranged in one of the front member and the rear member and includes: a recess extended longitudinally and shut off at least at its rear side end portion; and an engaging portion formed on the other and so inserted into the recess as to move longitudinally. A first bias member can be provided for biasing the rear member backward. Also, a second bias member can be arranged between the front member and the rear member for biasing the rear member backward with respect to the front member.
Preferably, either the front member or the rear member includes an engaging protrusion extended longitudinally whereas the other includes an assembly hole extended longitudinally for inserting the engaging protrusion slidably.
The vacuum type servo system can further include an elastically deformable engaging member that is deformed when the input member is moved backward by the reaction of the reaction member in accordance with the activation of the actuator for allowing the backward movement of the input member. The engaging member preferably engages the input member in accordance with the forward movement of the power piston with respect to the input member by the activation of the actuator, to move the input member and the atmospheric valve seat integrally with the power piston. The engaging member can engage the input member, when the actuator is activated at the inactive time of the input member to move the power piston forward with respect to the input member, so that in accordance with the activation of the actuator at the inactive time of the input member, the input member is moved backward by the reaction of the reaction member against a restoring force accompanying the elastic deformation of the engaging member, to bring the atmospheric valve seat and the atmospheric seal portion into abutment to thereby cut off communication between the rear chamber and the atmosphere.
The engaging member can be a key member engaging the power piston for moving longitudinally by a first predetermined stroke with respect to the power piston and with the input member for moving longitudinally by a second predetermined stroke with respect to the input member, wherein the housing includes a first opposed portion opposed to and able to abut against the rear face of the key member, wherein the power piston includes: a second opposed portion opposed to and enabled to abut against the front face of the key member; and a third opposed portion opposed to and enabled to abut against the rear face of the key member, and wherein the input member includes: a fourth opposed portion opposed to and enabled to abut against the front face of the key member; and a fifth opposed portion opposed to and enabled to abut against the rear face of the key member.
The vacuum type servo system can further include: a valve seat member arranged to move forward and backward with respect to the power piston independently of the movements of the input member and adapted to abut against the vacuum seal portion of the control valve for cutting off the communication between the front chamber and the rear chamber, wherein the rear member of the input member is integrally equipped with the atmospheric valve seat, and wherein the actuator moves the valve seat member backward to bring the valve seat member into abutment against the vacuum seal portion and moves the vacuum seal portion backward to bring the atmospheric seal portion apart from the atmospheric valve seat thereby to establish the communication between the rear chamber and the atmosphere.
The drive force of the actuator can be adjusted to adjust the output from the output member. The drive force of the actuator can also be adjusted to adjust the backward movement of the valve seat member with respect to the power piston. The actuator preferably includes a solenoid connected with an electric power source for attracting and moving the valve seat member backward when it receives the electric power, so that the output from the output member can be adjusted according to the attraction of the solenoid.
The valve seat member can be adjusted in its backward movement in accordance with the attraction of the solenoid and the vacuum type servo system can further include a third bias member arranged between the valve seat member and the power piston for biasing the valve seat member forward.
Another aspect of the invention involves a vacuum type servo system that includes: a housing having at least one pressure chamber formed therein; a movable wall so disposed in the housing as to move forward and backward with respect to the housing for partitioning the pressure chamber into a front chamber communicating with a vacuum source and a rear chamber selected to communicate with the front chamber and the atmosphere; a power piston jointed to the movable wall; an input member so arranged in the power piston as to move forward and backward with respect to the power piston; an atmospheric valve seat arranged in the power piston for moving forward and backward integrally with the input member; a vacuum valve seat arranged in the power piston; a control valve including an atmospheric seal portion capable of coming into and going out of abutment against the atmospheric valve seat for cutting off the communication with the rear chamber and the atmosphere when it comes into abutment against the atmospheric valve seat and for establishing the communication of the rear chamber with the atmosphere when it goes out of abutment against the atmospheric valve seat, and a vacuum seal portion capable of coming into and going out of abutment against the vacuum valve seat for cutting off the communication between the front chamber and the rear chamber when it comes into abutment against the vacuum valve seat and for establishing the communication of the rear chamber with the front chamber when it goes out of abutment against the vacuum valve seat; an output member for outputting the forward force of the power piston in accordance with the movement of the movable wall to the outside of the system; and a reaction member for transmitting the forward force of the power piston and an input fed to the input member, to the output member and for applying a reaction of a magnitude corresponding to an output of the output member, to move the input member backward, wherein the input member includes: a front member for coming into abutment against the reaction member; and a rear member capable of moving integrally with the atmospheric valve seat, so that when a predetermined input is fed to the input member, the rear member moves forward by a predetermined stroke with respect to the front member, and so that when the input member is moved backward by a reaction of the reaction member, the atmospheric valve seat and the atmospheric seal portion can come into abutment against each other to cut off the communication between the rear chamber and the atmosphere. The front member of the input member and the reaction member preferably abut in an initial state where no input is applied to the input member.
The present invention also provides a vacuum type servo system which includes: a housing having at least one pressure chamber formed therein; a movable wall disposed in the housing to be movable forward and backward with respect to the housing for partitioning the pressure chamber into a front chamber communicating with a negative pressure source and a rear chamber selected to communicate with the front chamber and the atmosphere; a power piston jointed to the movable wall; an input member arranged in the power piston to be movable forward and backward with respect to the power piston; an atmospheric valve seat arranged in the power piston to be movable forward and backward integrally with the input member; a vacuum valve seat arranged in the power piston; a control valve including: an atmospheric seal portion capable of coming into and going out of abutment against the atmospheric valve seat for cutting off the communication with the rear chamber and the atmosphere when it comes into abutment against the atmospheric valve seat and for establishing the communication of the rear chamber with the atmosphere when it moves out of abutment against the atmospheric valve seat; and a vacuum seal portion capable of coming into and going out of abutment against the vacuum valve seat for cutting off the communication between the front chamber and the rear chamber when it comes into abutment against the vacuum valve seat and for establishing the communication of the rear chamber with the front chamber when it goes out of abutment against the vacuum valve seat; an output member for outputting a forward force of the power piston in accordance with a movement of the movable wall to the an outside of the apparatus; and an actuator for bringing the atmospheric valve seat and the atmospheric seal portion away from each other to establish the communication between the rear chamber and the atmosphere, wherein a second predetermined input force is applied to the input member to be maintained at an inactive time of the actuator, so that an output force from the output member increases to a predetermined output force, and an output force generated by an activation of the actuator can be controlled from an output force, which is smaller than the predetermined output force.
Preferably, the vacuum type servo system also includes: a reaction member for transmitting a forward force of the power piston and an input force fed to the input member, to the output member and for applying a reaction force of a magnitude corresponding to an output force of the output member, to move the input member backward, and the atmospheric valve seat and the atmospheric seal portion can come into abutment against each other to cut off the communication between the rear chamber and the atmosphere when the input member is moved backward by a reaction force of the reaction member in accordance with the activation of the actuator.
When a predetermined input is fed to the input member, the rear member moves forward by a predetermined stroke with respect to the front member. When the input member is moved backward by a reaction of the reaction member in accordance with the activation of the actuator, the atmospheric valve seat and the atmospheric seal portion can come into abutment against each other to cut off the communication between the rear chamber and the atmosphere.
According to the present invention, the input member and the reaction member are in abutment against each other in an initial state where no input is applied to the input member. Also, the front member and the rear member are joined to each other by a first joint mechanism when the rear member moves forward by a predetermined stroke with respect to the front member, so that the front member and the rear member may integrally move forward, and the rearmost position of the rear member is regulated with respect to the front member whereas the front member and the rear member are jointed to each other by a second joint mechanism, when the rear member is at the rearmost position, so that the front member and the rear member may integrally move backward.
The front member can be longitudinally or axially moved with respect to the rear member by making the engaging portion longitudinally movable in the recess, and the backward movement of the rear member with respect to the front member is regulated by the abutment between the engaging portion and the rear side wall face of the recess. The rear member is preferably biased backward by a first bias member and the rear member is biased backward with respect to the front member by a second bias member.
The front member and the rear member are preferably engaged to move longitudinally relative to each other by inserting an engaging protrusion into an assembly hole. An engaging member is also adapted to be elastically deformed when the input member is moved backward by the reaction of the reaction member in accordance with the activation of the actuator, for allowing the backward movement of the input member. The engaging member engages the input member in accordance with the forward movement, as caused by the activation of the actuator, of the power piston with respect to the input member so that the input member and the atmospheric valve seat can move integrally with the power piston. The engaging member engages the input member, when the actuator is activated at the inactive time of the input member to move the power piston forward with respect to the input member. In accordance with the activation of the actuator at the inactive time of the input member, moreover, the input member is moved backward by the reaction of the reaction member against a restoring force accompanying the elastic deformation of the engaging member, to bring the atmospheric valve seat and the atmospheric seal portion into abutment thereby to cut off the communication between the rear chamber and the atmosphere. The engaging member is preferably a key member engaging the power piston for moving longitudinally by a first predetermined stroke with respect to the power piston and with the input member for moving longitudinally by a second predetermined stroke with respect to the input member. The housing includes a first opposed portion opposed to and enabled to abut against the rear face of the key member, wherein the power piston includes, a second opposed portion opposed to and enabled to abut against the front face of the key member; and a third opposed portion opposed to and enabled to abut against the rear face of the key member. The input member includes: a fourth opposed portion opposed to and enabled to abut against the front face of the key member; and a fifth opposed portion opposed to and enabled to abut against the rear face of the key member.
The actuator is adapted to move the valve seat member backward to bring the valve seat member into abutment against the vacuum seal portion and moves the vacuum seal portion backward to bring the atmospheric seal portion apart from the atmospheric valve seat thereby to establish the communication between the rear chamber and the atmosphere. The drive force of the actuator can be adjusted to adjust the output from the output member. The drive force of the actuator is adjusted to adjust the backward movement of the valve seat member with respect to the power piston, and the output from the output member can be adjusted according to the attraction of the solenoid.
The valve seat member is designed to be adjusted in its backward movement in accordance with the attraction of the solenoid and the valve seat member is biased forward by a third bias member arranged between the valve seal member and the power piston. When a predetermined input is fed to the input member, the rear member moves forward by a predetermined stroke with respect to the front member, and so that when the input member is moved backward by a reaction of the reaction member, the atmospheric valve seat and the atmospheric seal portion can come into abutment against each other to cut off communication between the rear chamber and the atmosphere.
According to the present invention, the front member of the input member and the reaction member abut in an initial state where no input is applied to the input member. A second predetermined input force is applied to the input member to be maintained at an inactive time of the actuator, so that an output force from the output member increases to a predetermined output force, and an output force generated by an activation of the actuator can be controlled from an output force which is smaller than the predetermined output force. The atmospheric valve seat and the atmospheric seal portion are adapted to come into abutment against each other to cut off communication between the rear chamber and the atmosphere when the input member is moved backward by a reaction force of the reaction member in accordance with the activation of the actuator.